mercury 150hp 1980.(lack of power when engine under strain)

[martyc123]

can any body help me,my mercury 150 seems to die but still runs when i rev it up when under strain.it also does not put charge in the battery.voltage in the batter stays the same when started,it sounds like it only fires on a few plugs when i rev it up on full power but sounds fine when on low revs.

 

[j_martin]

Re: mercury 150hp 1980.(lack of power when engine under strain)

The no charge deal is a bad rectifier or stator, probably the first.

High speed miss could be caused by that if your ignition system in general is marginal. Best bet would be to start at the bottom and diagnose it right.

1. Compression check. You can't fix a broken motor with electical or fuel parts.
2. Spark test at cranking.
3. DVA test of ignition system. CDI has a good guide for it, as does the Mercury factory service manual for your engine.
4. It doesn't sound like a fuel problem from the git go, but that would be next if nothing is found yet.

Proper diagnostics is the fastest and least expensive path to a repair, even if you have to buy a few tools to git er done.

hope it helps
John

 

[martyc123]

Re: mercury 150hp 1980.(lack of power when engine under strain)

hi,thanks for that john , today i tried a different stator and rectifier and was still the same.12.3 volts,same when started. also done a compresion test and was all ok,i dont know what you mean by ignition system in general is marginal??? and what is DVA test of ignition system , thanks

 

[j_martin]

Re: mercury 150hp 1980.(lack of power when engine under strain)

Enough with the throwing parts at it routine. It's ineffective and can be expensive, not to mention accidentally installing more problems.

You can test the rectifier, go or no-go with an ohmmeter. The procedure is in a FAQ on this web site.

Stator outputs are measured with a DVA (Direct Voltage Adapter) meter, which is a peak voltage integrator followed by a DC meter, usually in one device. Peak voltage is significant. RMS, as measured by the average meter means nothing in the diagnostics. Readings are in the factory manual, and are available at CDI's web site.

For now, with an ordinary AC voltmeter, you can disconnect the 2 yellow wires to the rectifier. Across those wires you should measure approximately 15V per 1000 rpm of engine speed.

The voltage problem may be just a wire broken under the insulation near a crimped connector. That same break would cause most Mercury rectifiers to short out as soon as the engine is sped up above idle.

If the ignition system is barely firing, the extra load of a shorted rectifier could lower the output of the charge coils (connected to the ignition) enough to cause misfire. If the ignition is in good shape, the slightly diminished output of the charge coils would not make a difference.

 

[martyc123]

Re: mercury 150hp 1980.(lack of power when engine under strain)

hi, if i disconect the rectifier ,will that stop the short if there is one and run ok and let the stator give the correct output to let the engine fire correct. correct me if i am wrong.this is the first time iv had a outboard that needs attention so im just a beginner.should i be putting the 2 yellow wires together when taking the reading from the rectifier ?, if there was a fault with the cdi will that stop me getting a reading from the yellows from the rectifier.should i get a ohm reading when i connect my meter to the 2 yellows from the stator when i take the stator off,thankyou